Cost-effective remote monitoring, diagnostic and system health prediction system and method for vapor compression and heat pump units based on compressor discharge line temperature sampling

ABSTRACT

A diagnostic monitoring system and method is employed for one or more vapor compression systems such as air conditioners and heat pumps having a compressor, an indoor air handler fan coil and an outdoor condensor. Temperature, voltage and current sensors are provided at the outdoor condensor to determine that at least one vapor compression system is operating properly. Data obtained from the sensors is wirelessly transmitted to a receiving-device for use by the systems&#39; custodian or repair service provider and includes information concerning an occurrence of periods when one or more of the vapor compression systems are operating at an abnormal state.

BACKGROUND AND SUMMARY OF THE INVENTION

The following terms and their acronyms are used hereinafter in thedescription of the invention:

-   -   Quality—the ratio of the mass of vapor to the total mass of a        saturated substance (see G. Van Wylen and R. Sonntag,        Fundamentals of Classical Thermodynamics, p. 37, (John Wiley &        Sons, 2nd ed., SI version 1978)).    -   Flow Quality—the ratio of the vapor mass flow rate to the total        mass flow rate.    -   Access Point (AP)—The device connected to the Internet to        transmit data between the Internet and any ED.    -   End Device (ED)—Any control or monitoring device located        remotely from the AP, which sends data or receives commands from        the AP,    -   OCU-ED—An Outdoor Condensing Unit End Device and sensors which        monitor performance of a split air-conditioning or heat pump        thermal control system.    -   IAH-ED—An indoor Air Handler Unit End Device and associated        sensors which monitors interior air temperature, and also can        monitor performance of the split air conditioner or heat pump        thermal control unit.    -   DHW-ED—A Domestic Hot Water Heater End Device and associated        sensors and relays which can monitor and control the hot water        temperature being supplied or stored in the hot water tank.    -   Remote Monitoring System (RMS)—The AP and any ED that        communicates with the AP.    -   Temperature Learning Range—In the currently preferred        embodiment, a range of at least 15° F. that will typically occur        between 70° F. and 95° F. For example, a data set with data        points collected at one degree increments from 72° F. to 87° F.        meets the criteria of the Temperature Learning Range.

The most basic vapor-compression refrigeration system consists of fourmajor components: compressor, evaporator, condenser, and expansiondevice. Actual practical hardware contains many other criticalcomponents for reliable, trouble-free operation, such as a controlsystem, high-pressure and low-pressure safety controls, liquid receiver,accumulator, oil separator, crankcase pressure regulator, etc., but thefour basic components are all that is needed to illustrate the functionof the basic system and the proposed improvement.

In a typical vapor compression system, refrigerant provides a coolingeffect as it evaporates, that is, as it boils and turns from liquid tovapor. For pure refrigerants and azeotropic mixtures, if the refrigerantevaporates at a constant pressure, then evaporation occurs at a constanttemperature while both liquid and vapor are present. Likewise,refrigerant rejects energy as it condenses from vapor to liquid. Forpure refrigerants and azeotropic mixtures, if the condensation occurs ata constant pressure, then the condensation will occur at a constanttemperature until all the vapor has condensed to a liquid. Therefore,for evaporation or condensation, the temperature and pressure arerelated by what is known as the pressure/temperature saturation curve.

In the conventional basic vapor compression cycle shown schematically inFIG. 1, subcooled liquid refrigerant 111 leaves the condenser 112 athigh pressure and flows to the throttling device 113 (capillary tube,TXV, etc.) where the pressure is decreased. The refrigerant then entersthe evaporator 114 as a two-phase mixture (liquid and vapor) andevaporates or boils at low temperature, thereby absorbing heat.Superheated refrigerant vapor 115 exits the evaporator and enters anelectrically-driven compressor 116 where the pressure and temperatureare increased as the compressor compresses the refrigerant vapor. Therefrigerant vapor leaving the compressor 117 is superheated, and thisrefrigerant is cooled and condensed in the condenser 112 where heat isrejected, and the refrigerant is condensed to liquid. Refrigeranttypically leaves the evaporator 114 slightly superheated (superheatvapor) to assure evaporation has been complete. Refrigerant typicallyleaves the condenser 112 slightly subcooled (subcooled liquid) to assurecondensation has been completed.

FIG. 2 schematically shows vapor compression system that is known as a“split” air conditioning system which is well known in the art. Itincludes an outdoor unit 20, also referred to as a condensing unit, andan indoor unit 40, also referred to as the fan coil unit or indoor airhandler, housed in a structure such as a residential home or acommercial building. The outside of the structure is denoted by numeral37 and the inside of the structure by numeral 38 with the structure'sexterior wall being denoted by numeral 39. The indoor (40) and outdoor(20) units are plumbed together via a liquid line 31 and a vapor line 35in a known way. A third approximately atmospheric pressure condensedwater drain line 36, also known as a condensate drain line, carrieswater 44 that condenses on the evaporator 42 and is captured in thedrain pain 45 of the indoor unit 40. This condensate water is thentransported to the outside 37 of the structure, typically to bedeposited on the ground 26 near the outdoor unit 20 to create moist wetsoil 54. The condensate drain line 36 carries the condensed water frominside 38 being cooled by the system to the outside 37 of the structure(typically by gravity assisted flow only), and is typically bundled withthe two refrigerant pipes 31,35 along with any control wires connectingthe controls of the indoor and outdoor unit (not shown).

The split system outdoor unit 20 typically includes a compressor 22,condensing coil 23, and cooling fan/motor unit 24 as well as othercomponents well known in the art and is typically located on a concreteor plastic slab or foundation 25 that rests on the ground 26. Standardoperation during the cooling season consists of superheated refrigerantvapor entering the condensing unit 20 via the vapor refrigerant line 35.The flow path consists of passing through the compressor 22 andcondenser 23, and exiting the outdoor unit 20 via liquid refrigerantconduit 31 and flowing to the indoor unit 40. The cooling fan/motor 24provides air flow across the condenser. The indoor unit consists of athrottling device 41 (such as a thermal expansion device, orifice plateor capillary tube), evaporator 42 and blower 43 as well as othercomponents well known in the art. Subcooled liquid refrigerant entersthe indoor unit 40, flowing to the expansion throttling device 41 andthen the evaporator 42 and normally exiting the evaporator assuperheated refrigerant vapor flowing back to the inlet of thecompressor 22 (which is located in the outdoor unit 20) through vaporrefrigerant line 35. Condensate, i.e. condensed water 44, flows bygravity (or by being pumped) in the condensate drain line 36 and exitsonto the ground 26 in a region near the outdoor unit 10. Those skilledin the art will understand the foregoing is only a very brief discussionof the operation of a split vapor compression air conditioning systemfor purpose of defining the condensing unit 20 and the purpose of theliquid line 31, compressor 22, vapor line 35, condenser 23, expansiondevice 41 and the evaporator 44 in such a system.

It is also well known in the art to use a reversing valve in the outdoorunit 20 along with check valves and two expansion valves to configurethe vapor compression system into a device that provides both coolingduring warm ambient temperatures and heating during cold ambientperiods. Such a vapor compression system, with a reversing valve, iscommonly referred to as a heat pump. For both a split air conditioningunit and a split heat pump there are two refrigerant lines connectingthe units, one containing condensed liquid refrigerant the othercontaining vapor refrigerant. In both cases, refrigerant vapor exitingthe evaporator flows to the compressor inlet and condensed refrigerantleaving the condenser flows to the throttling valve then on to theevaporator as more simply depicted in FIG. 1.

In a typical residential home, one of the largest sources of energyconsumption is the split vapor-compression air conditioning or heat pumpsystem described above (also hereafter referred to as the A/C unit). Ifthe A/C unit is operating at degraded efficiency, an equipment owner maybe unaware of the inefficiency because the equipment operates at ahigher duty cycle to maintain the house at the appropriate temperature.Eventually, an undetected equipment problem might lead to a costlysystem failure, such as a compressor motor burnout, or simply lead toincreased energy consumption, and failure to cool living spacesadequately during the next hot day.

A/C units that fail on the first unseasonably hot day of the year havetypically been operating at reduced capacity (at high duty cycles) forweeks or months. Although the energy bill is higher due to this degradedperformance, equipment owners either fail to notice the energy increaseor fail to relate the high energy bill to the A/C unit's degradedefficiency. An RMS that can detect degraded A/C unit performance priorto equipment damage or long periods of inefficient operation has obviousbenefits to the equipment owner, electric utility, and the environmentif such a unit is economical and reliable.

The HVAC service provider also benefits from an RMS by distributingservice calls more evenly. Currently, when the first hot days arrive andthe unit's degraded capacity becomes apparent, the equipment owner willcall a HVAC technician to service the A/C unit. However, the serviceprovider is usually overwhelmed with similar calls on the first hot daywhere system degradation becomes obvious. For the large servicecontractor firms with tens of thousands of service contracts, an RMSthat can predict failures before they occur or determine inefficientoperation has important benefits. The RMS also assists in the schedulingof service calls by providing detailed information regarding theseverity of the problem and by offering remote diagnosis. This allowsthe service provider to dispatch the appropriate repair technician tothe site and cluster similar service calls to a technician specializedin that repair.

There are many complex monitoring system approaches, such as the onedisclosed in U.S. Pat. No. 7,469,546 that includes the use oftemperature, pressure and flow sensors. Using pressure and flow sensorsdramatically increases the cost of the monitoring system and makes thistype of monitoring system unfeasible for residential or small commercialA/C units. A cost-effective RMS for residential or small commercial A/Cunits must eliminate expensive sensors and the labor-intensive processof plumbing the sensors into the refrigeration flow circuit. Flow metersand pressure transducers with sufficient accuracies that are includedwith the complex monitoring system are too expensive for thisapplication. To reduce costs to practical levels, the temperaturesensors that directly measure refrigerant temperatures (by being plumbeddirectly into the refrigerant flow loop) must also be replaced byexterior, surface mount temperature sensors. The in-loop temperaturesensors are significantly more expensive than surface mount sensors dueto the increased cost of a refrigerant-compatible and pressure-tolerantsensor and the additional cost to install these temperature sensors intothe refrigeration flow circuit.

In addition, for the typical split A/C unit or heat pump system, wherethe evaporator and blower are located inside the conditioned building(and referred to as the air handler or evaporator section) and thecondenser and compressor are located outside the conditioned space (andreferred to as the condensing unit), it is more difficult to monitorrefrigerant pressures, temperatures or flow rates on both the evaporatorsection and the condenser unit locations since they are not collocated.

U.S. Pat. No. 6,385,510 discusses a remote monitoring method where theconditioned air return temperature and return air humidity, along withthe supply air temperature and the system's design airflow rate andrated cooling capacity are used to monitor performance. Using thesystem's designed airflow rate can, however, introduce a significantamount of error as the air handler airflow rate is a function of thepressure differential across the blower. The geometry, length, orcircuiting of the air supply and return ducting will not be identical atall installations, altering the pressure differential across the blowerand, therefore, the blower airflow rate. An even larger inaccuracy couldbe created by the air filter, where there is a wide assortment of airfilters that impose different pressure drops and where pressure dropacross a filter will change over time due to the filter collectingparticles. If the air filter has become significantly clogged, the airhandler airflow rate decreases and then this monitoring system wouldthink that cooling capacity was enhanced due to the higher air enthalpychange when, in reality, cooling capacity has been diminished by aclogged air filter.

It is also well known in the art to have a server that is capable ofcommunicating with one or more remote locations, to send and receivedata from these remote units for the purpose of monitoring orcontrolling multiple devices. For example, U.S. Pat. No. 7,792,256discloses a system for remotely monitoring, controlling, and managingone or more remote premises.

We have discovered that there is a far more cost-effective way to doremote monitoring using compressor discharge sampling withoutsacrificing accuracy in predicting the health of the system beingmonitored. In order to appreciate just how significant our discovery is,however, some additional background discussion is useful.

It well known to those skilled in the art that when a fluid, such asrefrigerant in the evaporator of a vapor compression system of the typesshown in FIGS. 1 and 2, evaporates, that refrigerant does so at aconstant temperature as long as the pressure is constant. From amathematical perspective, the evaporating pressure and evaporatingtemperature are related and not independent. That is, for a specificrefrigerant, if the evaporating pressure is known, then the evaporatingtemperature can be determined by reference to that refrigerant's knownsaturation pressure temperature relationship which is valid only whenthe refrigerant is saturated. Once all the refrigerant liquid hasevaporated, additional heat input will cause the refrigerant temperatureto increase above saturation temperature and the refrigerant is referredto as being superheated. The numerical increase in the temperature ofthe refrigerant above the saturation temperature is referred to as thesuperheat of the refrigerant. That is the mathematical differencebetween the actual temperature and the saturation temperature (at thatpressure) is the superheat of the refrigerant.

For example, using the NIST Standard Reference Database 23, version 8.0software program titled REFPROP, available from the US Department ofCommerce; the saturation temperature of Refrigerant 134a at 40 psia is29 degrees F. If the refrigerant has been heated to 34 degrees F., (andthe pressure held at 40 psia) then the superheat would be 5 degrees F.

Therefore, we recognized when examining the condition of the refrigerantexiting the evaporator, with only a temperature sensor, the diagnosticvalue of the knowing both the temperature and pressure at this exit canbe undesirably limited. If the temperature is above the saturationtemperature, as in the case just discussed when the refrigerant issuperheated, then the exit enthalpy, or similarly the thermodynamicstate point, can be determined. However, if the temperature exiting theevaporator is the saturation temperature (for the measured pressure),then it is not possible to determine the flow quality from only thesetwo measurements. That it, is not possible to determine if therefrigerant flowing from the evaporator outlet is nearly all liquid,nearly all vapor, or some other saturated condition. Without thisknowledge of the flow quality, the thermodynamic state point or the exitenthalpy of the saturated refrigerant exiting the evaporator outletcannot be determined. This also means the effectiveness of theevaporator at evaporating the entire refrigerant, cannot be determinedwith only the exit pressure and temperature measurements, if refrigerantis leaving the evaporator in a saturated condition. It is for thisreason, that thermal expansion valves and other feedback expansiondevices are necessary to monitor exit superheat, and the evaporators ofthese systems are designed to have superheated refrigerant exit theevaporator. This exit superheat is typically very small, since theprimary function of the evaporator is to vaporize refrigerant. Undercertain fault conditions, the superheat may be excessive, such as whenthe refrigerant charge is low, in other cases the superheat may benegligible or the evaporator exit may be saturated. When the refrigerantexits the evaporator as a saturated refrigerant, it is not possible todetermine the quality that is the relative amount of vapor and liquidrefrigerant exiting the evaporator; hence, it is also not possible todetermine how much the cooling capacity of the evaporator has beendegraded.

The foregoing point is most easily demonstrated by the followingexample. For a unit mass of refrigerant, the heat absorbed byevaporation, i.e., the heat of vaporization is much greater that theheat capacity of a single phase superheated refrigerant. In the case,for example, of above-mentioned Refrigerant 134a and using REFPROP onceagain, the energy to evaporate one pound of Refrigerant 134a fromsaturated liquid to saturated vapor (at a saturation pressure of 40psia, saturation temperature of 29 degrees F.), namely the latent heatof vaporization is 86.0 BTU/LB, whereas the energy to raise thetemperature of the refrigerant from the saturation temperature of 29degrees F. to 34 degrees (5 degrees F. of superheat) is only 1.1 BTU/LBor only 1.3% of the latent heat of vaporization (1.1/86). Likewise, theenergy to raise the temperature of the refrigerant from the saturationtemperature of 29 degrees F. to 39 degrees (10 degrees F. of superheat)is only 2.1 BTU/LB or 2.4% (2.1/86). Therefore if the cooling providedby evaporation increased by about 1% (energy into the evaporatorincreased by 1%) the superheat would increase from 5 degrees F. to about10 degrees F., and therefore this increase could be easily determined bya noticeable temperature change of 5 degrees F.

If, however, the cooling provided by evaporation decreased by anythingmore than about 1% (energy into the evaporator decreased by more than1%) there would be no superheat at the exit; rather the refrigerantwould be leaving the evaporator at saturated conditions, in the case ofthis example, 29 degrees F. The two important points to be made here are(1) by simply monitoring the temperature in the conventional way it isnot possible to determine if the cooling (namely the evaporation in theevaporator) has decreased by 1% or 90%, since the refrigerant exitingthe system would be saturated and therefore at the same temperature, and(2) a very accurate measurement of the temperature at the outlet of theevaporator is necessary if one has any hope of determining any reductionin cooling capacity, since a 5 degree reduction in outlet temperature isonly a 1% reduction in capacity and, once saturated outlet conditionsare achieved, no further temperature measurements are useful.

We have discovered an inexpensive diagnostic method that makes itpossible to identify reductions in cooling before they becomesignificant and to provide this diagnostic warning at minimal cost. Toreduce cost, all measurements are collected at a single location, namelythe condensing unit, without the need to install sensors inside thestructure being cooled or on the indoor air handling unit. While ourmethod could measure the refrigerant temperature at the inlet to thecompressor, which represents the first component downstream of theoutlet of the evaporator, or measure the temperature anywhere in therefrigerant line between the evaporator outlet and the compressor inlet,we recognized that even small heat transfer with the ambient couldaffect an accurate reading of the superheat temperature and ifincomplete evaporation were occurring, the same inability to determinethe flow quality, with only a temperature measurement would still bepresent.

We have discovered another and far superior method of determining areduction in the evaporation at the outlet of the evaporator that onlyrelies on a temperature measurement, but can still determine therelative amount of saturated vapor, that is the relative quality,exiting the evaporator. Since, as we recognized, the compressor normallyinputs a relative constant amount of energy into the refrigerant (for aspecific outdoor air temperature), and the refrigerant always exits thecompressor as a superheated vapor, by investigating the temperature atthe outlet of the compressor, that is by looking at the compressordischarge temperature, the relative amount of evaporation in theevaporator can be easily determined. If the refrigerant exits theevaporator with a low thermodynamic flow quality, meaning a largefraction of saturated liquid is leaving the evaporator, the temperatureat the outlet of the compressor will be lower. Likewise if therefrigerant exits the evaporator with a high thermodynamic flow quality,meaning a small fraction of saturated liquid is leaving the evaporator,the temperature rise at the outlet of the compressor will be fargreater, and if the refrigerant exits the evaporator as a superheatedvapor, the temperature rise at the outlet of the compressor will be evenmore. Once again an example from REFPROP may be useful.

If 1 pound per hour of R-134a refrigerant (at 40 psia) leaves theevaporator with a quality of 0.5 (half vapor by mass) which representsan exit enthalpy of 128.1 BTU/lb and has the compressor input 60 BTU/hrof energy into the system, the refrigerant will be discharged from thecompressor with an enthalpy of 188.1 BTU/Lb. If the pressure at thecompressor discharge is 140 psia, then the refrigerant is dischargingthe compressor at a temperature of 131.6 degrees F.

Alternatively, if 1 pound per hour of R-134a refrigerant (at 40 psia)leaves the evaporator with a quality of 0.9 (90% vapor by mass), whichrepresents an exit enthalpy of 162.5 BTU/lb and has the same compressorenergy input of 60 BTU/hr into the system, the refrigerant willdischarge the compressor with an enthalpy of 222.5 BTU/Lb. If thepressure at the compressor discharge is again 140 psia, then therefrigerant is now being discharged from the compressor at a temperatureof 269.5 degrees F. A 137.9 degree F. increase occurs due to the qualitychange from 0.5 to 0.9. Finally, if 1 pound per hour of R-134arefrigerant (at 40 psia) leaves the evaporator with a superheat of 5degrees F. (exit temperature of 34 degrees F. and pressure of 40 psia),which represents an exit enthalpy of 172.1 BTU/lb and has the compressorinputs the same 60 BTU/hr of energy into the system, the refrigerantwill be discharged from the compressor with an enthalpy of 232.1 BTU/Lb.If the pressure at the compressor discharge is again 140 psia, then therefrigerant is now being discharged from the compressor at a temperatureof 306 degrees F. A 36.5 degree F. increase due to a change from asaturated at a quality of 0.9 to superheated 5 degrees F.

As the foregoing example clearly demonstrates, by measuring thetemperature at the compressor discharge, rather than the evaporatorinlet, the effects of different evaporator exit conditions, is greatlyamplified. This simplifies the measurement and less accurate temperaturemeasurements on the exterior of the tube can be used since thetemperature differences are much larger than the typical 5 degree F.variation at the evaporator outlet (between superheated evaporatordischarge and a saturated discharge). Also by measuring the temperatureat the compressor discharge, different evaporator exit qualities, i.e.,different levels of evaporation can also be determined from thecorresponding compressor discharge temperature.

Hence, one object of the present invention is to provide a reliable,low-cost vapor-compression air-conditioning and heat pump monitoringsystem that can reliably predict equipment failures and determinelow-efficiency operation. This monitoring system can be located entirelyin the outdoor condensing unit, without the need to place any sensorsinside the building or inside the indoor portion of the split airconditioning or heat pump unit. This greatly simplifies installation andlowers cost.

The present invention disclosed herein utilizes only three temperaturesensors, a current sensor, and three voltage sensors. Two of thetemperature sensors are mounted on the exterior surfaces of pipeslocated in the outdoor condensing unit, while the last temperaturesensor measures outdoor air temperature. The tube-mounted temperaturesensors are located on the compressor discharge tube and the condenseroutlet tube. The current draw of the compressor or the total current tothe condensing unit, which includes the power to both the compressor andthe condenser fan, is also measured to identify potential problems. Twovoltage measurements (Run Winding Voltage, Start Winding Voltage), arealso used. Optionally, the inlet voltage can also be measured, to verifythe status of the condensing unit's contactor (relay). With thisinformation, the system, according to the present invention, canautomatically learn the characteristics of the specific vaporcompression system, then monitor the system for future problems,including faulty run or start capacitance operation, low refrigerantcharge, reduced condenser airflow or reduced evaporator airflow. Inaddition to split air conditioning or heat pump systems, this samediagnostic approach can be applied to any vapor-compression system,including refrigerators, freezers and the like.

We have developed a family of novel diagnostic algorithms to enable theidentification of all common mechanical problems, electrical problems,and maintenance issues. These algorithms have been designed to be verysimple, thereby allowing the analysis to be performed on site or at aremote location, by transferring the data via the internet or othermeans, or by using a combination of both on-site and remote analysis toallow reduced data traffic, safe storage of the data, and reduced serverloading.

In one currently preferred embodiment, the system consists of an indoorAP device which provides communication between the OCU-ED and the servercomputer, located at a remote location and connected via the Internet orother appropriate communications system. The OCU-ED can be installedquickly on the condensing unit without any modifications to the plumbingor condensing unit since measurements are obtained on external tubesurfaces in the outdoor condensing unit, the ambient outdoor air, fromvoltage measurements from capacitors and contactor connection surfacesin the outdoor unit, or from current draw of a compressor or overalloutdoor condensing unit power supply conductor either of which is routedthrough a current sensor.

The AP device of the present invention would also allow additional enddevices to be located in the building. For example, a second end device,referred to here as the IAH-ED, could be used to monitor the indoor airtemperature returning to the air handler and can therefore provide athermostatic like thermal control effect, to override the existingthermostat and provide precise temperature control based on instructionsfrom the AP. That is, a programmable thermostatic effect, selected viathe Web-based interface and transmitted by the AP to this end device,could be used to control the room air temperature. Likewise, one skilledin the art could extend this invention to other items in the home, suchas for example a DHW-ED, which along with associated sensor and relay,can monitor and control the domestic hot water supply temperature basedon instructions from the AP. That is a programmable time-dependentthermostatically-controlled hot water heater effect, selected via theWeb-based interface and transmitted by the AP to this DHW-ED, could beused to monitor and control the domestic hot water supply temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become more readily apparent from the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIG. 1 is a highly simplified schematic diagram of the conventionalelectrically-powered vapor compression unit described above.

FIG. 2 is a schematic view of the known vapor compression split A/C unitdescribed above.

FIG. 3 is a schematic diagram showing information flow in the currentlypreferred embodiment described in detail herein below.

FIG. 4 is a basic high-level diagram of one currently contemplatedembodiment of the OCU-ED in connection with the present invention.

FIG. 5 is a graph which displays the variation of refrigeranttemperature at the compressor discharge for a range of indoor andoutdoor air temperatures of a properly operating A/C unit.

FIG. 6 is a graph which shows an example of identifying low refrigerantcharge using the compressor discharge temperature by comparing themeasured value to the baseline curve of various system faults.

FIG. 7 is a graph which displays the variation of refrigeranttemperature at the condenser outlet for a range of indoor and outdoorair temperatures of a properly operating A/C unit

FIG. 8 is a graph which shows an example of identifying low condenserairflow using the condenser outlet (liquid line) refrigerant temperatureby comparing the measured value to the baseline curve of various systemfaults.

FIG. 9 is a graph which shows the variation of winding voltage ratio tocurrent at normal and degraded run capacitor capacitances for acondensing unit.

FIG. 10 is a flow chart which shows steps to collect the baseline datafor the currently preferred embodiment.

FIG. 11 is a flow chart which shows the current preferred method tocompare the measured data with the baseline performance curves.

DETAILED DESCRIPTION OF THE DRAWINGS

A basic RMS consists of a minimum of two components: the OCU-EDinstalled on the outdoor condensing unit of a typical residential (orsmall commercial) split A/C or heat pump system (or a unitary system)and the AP providing a bi-directional communications link. The AP is anInternet bridge that communicates with any remote device in the home(such as the OCU-ED) and transmits the communication via the Internet toa web-based monitoring site. The OCU-ED performs A/C unit datacollection and some on-site analysis. This collected data is thentransmitted to the AP and sent to the web-based server for dataprocessing, storage, and analysis.

The OCU-ED of the RMS system is designed to monitor A/C unit parametersdaily and provide early detection of maintenance issues (dirty condensercoil, dirty air filter, etc.) and service repair issues (such as lowrefrigerant charge, failed run or start capacitor, faulty fans orblowers, short cycling, etc.). When a problem is detected, the systemwill automatically notify the equipment owner and the HVAC service andrepair company (hereafter referred to as the repair service provider)that installed the RMS.

The AP gateway serves as a pass-through for data and will be configuredto collect the data from the remote devices and pass it to the centralserver via standard Internet protocols.

FIG. 3 shows a currently preferred embodiment of the overall systemcommunication and the basic information flow. This type of architectureis particularly preferred in the field because it allows for scalabilityfor structures with multiple A/C units or additional end devices. Thesystem takes advantage of wireless mesh networking to pass messagesbetween end devices and the access point even when the origin anddestination are not within transmitting reach of each other. End devicesare able to directly query each other to determine operating parameters,sensor readings, and other information determined to be relevant by anED.

FIG. 4 shows the currently preferred embodiment of the OutdoorCondensing Unit End Device (OCU-ED). The OCU-ED electronics areseparated into two sides, one for high voltage signals and the other forlow voltage signals. The two sides are galvanically isolated to reduceshock risk to users. On the high voltage side there is the analogportion, a microcontroller and the power supply. The analog portionmonitors 3 high voltage signals and one current signal fed to a burdenresistor from a current transformer. These signals are scaled andshifted from AC signals to low voltage DC signals using a differentialamplifier circuit. The signal is then filtered with a low pass filterand sent to the microcontroller's analog to digital converters foranalysis.

The microcontroller reads each signal at multiple kilohertz with itsanalog to digital converter. The original signal values are thenextracted from the results of the analog to digital converter usingpreviously determined calibration data. The original signal values aresent to the low side through an isolated serial connection to beanalyzed.

The power supply is powered off the line voltage supplied to thecondensing unit and the power takeoff is located upstream of thecontactor which closes to power the compressor so that this circuit isalways hot. The power supply provides low voltage DC power to each sideof the board.

On the low voltage side is a wireless transceiver microcontroller, an RFfront end IC, antenna, thermistor inputs and user interface components.

The wireless transceiver microcontroller used in the preferredembodiment is the CC2530. Connected to the Radio of the CC2530 is the RFfront end IC. This IC increases transmitter power and receiversensitivity to increase the communication range. The CC2591 is used forthe RF front end. Connected to the CC2591 is a PCB mount antenna.

Negative temperature coefficient thermistors are connected to themicrocontroller's analog to digital converter through a voltage dividerand a low pass filter. LED light signals are used to provide basicstatus information to the user. A button is also connected to themicrocontroller to give the user basic control.

Algorithms were developed to detect performance degradation in a vaporcompression system using a minimum of only three temperaturemeasurements, three voltage readings, and a current measurement. As aresult, no pressure transducers or flow meters are required for accuratemonitoring. Eliminating pressure transducers was essential because theycan become a source of refrigerant leaks (due to vibration,under-tightening, or over-tightening), and are cost prohibitive.Additionally, pressure transducers exhibit calibration drift over time,with decreasing monitoring accuracy. The temperature measurements beingused in this invention can employ inexpensive, rugged thermistors, orsimilar low cost temperature sensors, which in the case of thermistorschange resistance with temperature and therefore are subject tonegligible calibration drift.

Other inexpensive temperature sensors can be used and is well known inthe sensing art. The current transducer and voltage sensors are alsoinexpensive and very reliable. Since performance degradation or failureprediction is determined by a change in performance over time, sensorrepeatability is critical. Sensors need not be calibrated to specificabsolute values. The temperature sensors need only be located on theexternal surfaces of the refrigerant tubing, rather than directly incontact with the refrigerant, and their exact placement on thecompressor discharge tube or condenser outlet tube is not critical, aslong as they are near enough to these devices to provide propermeasurements without being affected by external factors such assunlight.

In our currently preferred embodiment, sensor data obtained by theOCU-ED is processed locally to determine general A/C unit performancecharacteristics and uploaded to a web server where more detailedanalysis can be optionally performed. The frequency of the upload isdetermined from the results of the local OCU-ED data analysis. In thecurrent embodiment, the minimum upload frequency is once per day, andthe maximum upload frequency is once every time the unit cycles off (orevery hour if it operates for more than 1 hour continuously). Systemsoperating near alarm values upload data more frequently. The RMSmethodology requires collecting baseline data immediately afterinstallation or tune-up servicing by an HVAC professional (when thesystem is assumed to be operating properly). The OCU-ED collectsbaseline data and automatically calculates a performance model thatdescribes proper performance as a function of outdoor air temperaturefor that individual A/C unit. A complete set of baseline data includes:(1) a curve of compressor discharge temperatures (on the externalsurface of the tubing) verses outdoor air temperature, developed fromdata collected while operating within the outdoor Temperature LearningRange, (2) a curve of condenser outlet (liquid line) temperature (on theexternal surface of the tubing) verses outdoor air temperature developedfrom data collected while operating within the outdoor TemperatureLearning Range, (3) a curve of compressor, or condensing unit, currentdraw verses outdoor air temperature, developed from data collected whileoperating within the outdoor Temperature Learning Range, and (4) a curveof start winding voltage divided by run winding voltage (or the inverse)verses total current, developed from data collected while operatingwithin the outdoor Temperature Learning Range.

After a complete set of baseline data is collected, a family ofequations to define normal operation is developed and used to compareagainst all future measured data. System alarms are triggered when datapoints consistently fall outside of the acceptable range of operation.This methodology has been tested and demonstrated to successfully learnthe A/C unit characteristics and subsequently monitor futureperformance. Details of this algorithm and the results of experimentsare set forth below.

Typical failure modes that occur in a residential or small commercialA/C unit include:

-   -   1. Loss of Refrigerant Charge—An A/C unit with a slow leak can        operate inefficiently for months or years before it is incapable        of maintaining the desired indoor air temperature on a very hot        day. Before this A/C unit failure, the loss of cooling capacity        is masked by higher A/C unit duty cycle and additional energy        consumption. Unfortunately, by the time the capacity and        efficiency degradation is typically identified by the equipment        owner, the system has been wasting energy for months, if not        years. In addition, if a refrigerant leak is not identified        prior to a significant loss of refrigerant, a complete failure        (compressor failure) or iced-up evaporator can occur, resulting        in a total loss of cooling capacity and potentially significant        damage to the A/C unit or home (mold growth).    -   2. Degraded Run Capacitor—The capacitance of the Run Capacitor        typically diminishes over time due to various factors, such as        leaking electrolyte or reduced foil capacitance. This        degradation cannot be identified visually since no physical        evidence of electrolyte leaking is visible. This decrease in        capacitance reduces the starting torque developed by the        compressor's motor, and at some point the compressor will no        longer start. This failure often occurs on the first hot day of        the year as the required starting torque increases with outside        air temperature. Once again, these symptoms are unknown to the        equipment owner until the compressor will not start on one of        the hottest days of the year.    -   3. Faulty Potential Relay or Degraded Start Capacitor—When        included with a system, and working properly, the Start        Capacitor is connected to the start winding circuit for        milliseconds by the Potential Relay during compressor start-up.        This provides increased starting torque to help start the        compressor motor. Like a degraded Run Capacitor, a degraded        Start Capacitor or a faded Potential Relay will lower the        starting torque developed by the compressor's motor. At some        point the compressor will no longer start, resulting in total        loss of cooling. The starting torque required increases with        outside air temperature; this is another problem that has        symptoms the equipment owner can't detect until the compressor        will not start, likely on one of the hottest days of the year.    -   4. Blocked or Restricted Condenser Airflow—Low condenser coil        airflow can be caused by a dirty condenser coil, overgrown        plants around the condensing unit, or the condenser fan blade        rubbing on the housing. Low condenser airflow will require the        compressor to consume more energy (along with a decrease in A/C        cooling capacity) since the condenser saturation temperature        must be higher to achieve the same heat rejection. This lowers        the performance of the unit, accelerates damaging acid        formation, and shortens the life of the A/C unit (from both an        acid and mechanical degradation standpoint). Additionally,        reduced condenser airflow could reduce the life of the condenser        fan due to increased motor load and reduced motor cooling        airflow. While the equipment owner may be able to detect the        noise of a rubbing condenser fan or clearly see an obstructed        airflow path, most equipment owners rarely inspect their        condensing unit visually.    -   5. Blocked or Restricted Evaporator Airflow—Slight changes in        airflow, which could be caused by a change in air filter type or        quality of the filter, are normal and must not be flagged as an        alarm. For example, the airflow rate though a MERV 11 pleated        filter is far less than the airflow through an expensive MERV 6        fiberglass mat filter, and the equipment owner could switch        filter types monthly or seasonally. Significant loss of airflow        however, should be identified as a problem.    -   6. Pitted Contactor—The Contactor is a relay that provides power        to the Outdoor Condensing Unit when the thermostat calls for        cooling. Pitted electrical contact surfaces on the Contactor        make a poor electrical connection, causing electrical resistance        and a voltage drop to the electrical components in the        condensing unit (compressor and fan). This voltage drop        increases current and causes substantial heating of the        Contactor's electrical contact surfaces, resulting in further        pitting of the Contactor. The reduced voltage caused by the        pitted Contactor will lower the voltage to the compressor and        blower fan, resulting in lower starting and operating torque to        these electric motors, eventually reaching a point where they        can no longer operate. In the preferred configuration, the RMS        should detect a pitted Contactor.

In order to create these common faults and provide examples of thecapability of the disclosed invention herein, a 3-ton A/C unit wasplaced into an environmental chamber and operated under normal and faultconditions. Table 1 below provides a summary of the common faultscreated on this system.

TABLE 1 A/C unit operating conditions tested Refrigerant Indoor AirOutdoor Air Test Condition Air Filter Condenser Charge Temp (° F.) Temp(° F.) Normal Operation Clean Clean Proper charge 71-85 80-95Dirty/Blocked Condenser Clean 18% blocked Proper charge 72-76 80-95Dirty/Blocked Condenser Clean 37% blocked Proper charge 71-85 80-95Dirty/Blocked Condenser Clean 55% blocked Proper charge 71-85 80-95Dirty/Blocked Air Filter 17% Blocked Clean Proper charge 71-73 80-95Dirty/Blocked Air Filter 37% Locked Clean Proper charge 73-77 80-95Dirty/Blocked Air Filter 55% Blocked Clean Proper charge 71-85 80-95Dirty/Blocked Air Filter 73% Blocked Clean Proper charge 71-85 80-95 LowRefrigerant Charge Clean Clean 1 LB low 71-85 80-95 Low RefrigerantCharge Clean Clean 2 LB low 71-85 80-95 Low Refrigerant Charge CleanClean 3 LB low 71-85 80-95 Refrigerant Overcharged Clean Clean 1 LB high79 90 Refrigerant Overcharged Clean Clean 2 LB high 81 90 RefrigerantOvercharged Clean Clean 3 LB high 76-82 90-92 Refrigerant OverchargedClean Clean 4 LB high 74-82 87-90

To minimize cost and installation time, we have discovered that thefollowing sensors commonly used in remote monitoring and systemdiagnostic procedures are not required for accurate health andperformance predictions using our approach. The elimination of thesesensor data simplifies installation, lowers cost, and improvesreliability of the monitoring system.

-   -   Indoor air temperatures—While typical remote monitoring devices        monitor indoor air temperature (evaporator inlet air        temperature) as well as evaporator air exit temperature, we have        found that monitoring these temperatures is not necessary for        detection of potential faults in the system. Since the currently        preferred embodiment for the remote monitoring locates the        OCU-ED outside (at the condensing unit), indoor air temperature        monitoring and/or evaporator discharge air temperature        monitoring would add significant cost to the unit and        unnecessary complexity to the installation.    -   Condenser discharge air temperature—While some remote monitoring        devices monitor condenser inlet air temperature, which is the        outdoor air temperature, as well as condenser discharge air        temperature, we have found that that only outdoor air        temperature needs to be measured. We have also discovered that        spatial temperature gradients in the condenser air discharge        also make the condenser discharge air temperature measurements        inaccurate. The use of the additional temperature sensor would        also add unneeded cost, inaccuracy, and complexity to the        system.    -   Condenser Refrigerant Inlet and Outlet Temperature—Some remote        monitoring devices monitor the enthalpy change of the        refrigerant entering and exiting the condenser, or estimate this        enthalpy change by measuring the temperature change across the        condenser. However, we have discovered a monitoring and fault        prediction method that does not require these temperature        measurements; rather only the surface temperature of the        condenser discharge piping needs to be measured as a function of        outdoor temperature. The use of the temperature sensors in the        refrigerant flow would likewise add cost and installation        complexity.    -   Evaporator Refrigerant Inlet and Outlet Temperature—Typically,        the conventional method of determining low refrigerant charge in        a fixed expansion device, such as a capillary tube or orifice        plate expansion device, is to measure the evaporator saturation        temperature or pressure and evaporator discharge temperature so        that evaporator superheat can be determined. Evaporator        superheat is also the conventional method of determining a dirty        evaporator, clogged air filter, and poorly operating evaporator        blower. Evaporator superheat is the difference between        evaporator discharge temperature and evaporator saturation        temperature. Therefore, conventional monitoring devices        typically monitor the temperature of the refrigerant entering        and exiting the evaporator; however, we have discovered a        monitoring and fault prediction method that does not require        these temperature measurements. Once again, the use of the        temperature sensors in the refrigerant flow would add cost and        installation complexity. In addition, as stated earlier, since        the currently preferred embodiment for the remote monitoring is        to locate the OCU-ED outside (within the condensing unit),        indoor refrigerant temperature monitoring would add significant        cost to the unit and complexity to the installation.    -   Refrigerant temperature at the compressor suction—Although we        have discovered that compressor suction temperature is one        potential indicator of insufficient charge, we have further        discovered that the compressor discharge temperature is        dramatically affected by compressor suction temperature, and        amplifies the effect. Monitoring the compressor discharge        temperature thereby provides a more pronounced indication of        system charge effects, and thereby provides for a dramatically        improved sensitivity, without the need to dramatically improve        the sensitivity and cost of the actual temperature sensor. This        amplified affect allows the use of an external temperature        measurement on the surface of the compressor discharge tubing        rather than requiring a temperature measurement directly in the        refrigerant stream.    -   Compressor can temperature—Typically, a conventional method of        determining improper charge or poor evaporator performance has        been to monitor the external compressor housing of a hermetic        compressor (typically referred to as the compressor can).        However, we have discovered that the temperature (at any        location on the compressor can) cannot be used in performance        monitoring because of significant fluctuations due to the        boiling of liquid refrigerant in the compressor housing. The        amount of liquid refrigerant in the compressor can housing and        the rate at which it evaporates is a function of many variables,        some which cannot be accurately measured or known.    -   Refrigerant pressure (high-side and low-side)—Essentially all        monitoring of a vapor compression system performance has        traditionally relied on the measurement of the refrigerant        pressures on the low- and high-sides of the system. For example,        the first thing a refrigeration technician is trained to do        during a service call is to connect a manifold gauge set to        visually inspect the operating pressures. Unfortunately, as        stated earlier, this adds significant component cost,        installation cost and complexity, and calibration drift.        Although these pressures can be used to analyze the system, we        have discovered an alternative method that does not require the        use of pressure measurements for accurate health monitoring or        fault prediction.        The Fault Detection Method of the Present Invention        Failure Mode 1: Low Refrigerant Charge

To detect low refrigerant charge, a baseline curve of compressordischarge temperature (measured on the external surface of the dischargepiping to reduce cost) versus outdoor ambient temperature is developedby collecting data during the learning period. After sufficient baselinedata has been collected over a range of outdoor air temperatures, abest-fit polynomial is automatically calculated. This baseline best-fitpolynomial allows the OCU-ED to calculate the typical compressordischarge temperature for any outdoor air temperature. When the measuredcompressor discharge temperature is between 25° F. and 45° F. above thepredicted value from the baseline curve, then a low-priority warning oflow-charge is indicated. If the measured discharge temperature is morethan 45° F. above the predicted value from the baseline curve, then ahigh-priority (imminent failure) warning of low-charge is indicated. Itwill now be understood by one skilled in the art that a key to thisinvention is the use of the temperature of the external surface of therefrigerant line at the compressor discharge as an indicator of systemproblems. The actual variation to be used to detect a problem isdependent on the level of detection desired by the designer. It is alsocontemplated that compressor inlet temperature could be used instead ofcompressor discharge temperature; however, we have discovered that thecompressor discharge temperature variation is more sensitive tolow-charge and will indicate a problem earlier. The relativeinsensitivity of this configuration to the exact location of sensors,due to the baseline performance being developed after the sensors arelocated, is the case for all the sensors used in this invention. Ofcourse, normal sensor positioning practices that are well known in theart, must be followed, namely the sensor should be located on the sidesof the tube, and should avoid being located at the top or bottom of thetube.

Example 1 Demonstrating the Capability to Identify Low RefrigerantCharge

In addition to decreasing the life of an A/C unit and wasting electricalpower by decreasing A/C unit cooling capacity, a low refrigerant chargeindicates a leak in the system that is venting a greenhouse gas whichhas a high global warming potential into the atmosphere. Early detectionof refrigerant leaks could significantly decrease the amount of HCFCsand HFCs in the atmosphere, and reduce global warming and greenhouse gasemissions. Low-refrigerant charge is one of the most common A/C unitservice problems, causing numerous insufficient cooling service calls onthe first hot day of the year. This surge of service calls on the sameday presents a problem to HVAC service contractors because they are notstaffed to respond to all the calls in a timely manner.

FIG. 5. Since indoor air temperature is not monitored in this RMSembodiment, a low refrigerant charge alarm will only occur when thecompressor discharge refrigerant temperature is at least 25° F. warmerthan the baseline polynomial calculates. This will prevent false alarmsfrom occurring due to the 15° F. compressor discharge refrigeranttemperature range that could occur under normal operation.

FIG. 6 displays baseline performance, non-critical alarm, and criticalalarm curves for a 3-ton split air conditioning system. The equation forthe second-order baseline polynomial is:Baseline=−0.0347T _(amb) ²+6.7064T _(amb)−185.05Where T_(amb) is the outdoor ambient air temperature in degreesFahrenheit.

Using this equation, the OCU-ED can compare any future compressordischarge temperature to the expected value (determined at thatparticular outdoor ambient air temperature). The non-critical low chargealarm curve and critical low charge alarm curve y-intercepts are 25° F.and 45° F. greater than the baseline y-intercept value, respectively.Non-Critical Low-Charge Alarm=Baseline+25orNon-Critical Low-Charge Alarm=−0.0347T _(amb) ²+6.7064T _(amb)−160.05Critical Low-Charge Alarm=baseline+45orCritical Low-Charge Alarm==−0.0347T _(amb) ²+6.7064T _(amb)−140.05

FIG. 6 displays the compressor discharge refrigerant temperature underseveral inefficient or failure conditions. The loss of 1, 2, or 3 poundsof refrigerant will increase compressor discharge temperatures by 35°F., 75° F., or 120° F., respectively, and the other system faults ofTable 1 are clearly differentiated from the low refrigerant charge data(as will be discussed below).

Since the RMS function is to identify a problem as quickly as possible(while eliminating the possibility of false negatives), the RMSmicroprocessor need only identify compressor discharge temperatures thatare more than 25° F. greater than the baseline curve. A compressordischarge temperature that is more than 25° F. above the baselineindicates that the cooling capacity has decreased by at least 13%, andthe coefficient of performance has been reduced by at least 5%.Therefore, it is clear that we can detect very small losses inrefrigerant (under one pound loss of charge) as well as the resultingloss of cooling capacity (13%), which would be undetectable by theequipment owner due to higher A/C unit duty cycle. Likewise, anefficiency degradation of 5% might not be detected by equipment ownerson their energy bill, but will be detected by the RMS according to thepresent invention before the problem worsens. These very smallreductions in performance can be detected by the RMS while avoiding thepotential for false positives. Note that the maximum temperaturedifferential that can exist due to variations in the unknown interiorair temperature is only 15° F. and the 25° F. variation above thebaseline was selected to be well above the potential 15° F. normalvariation due to different possible normal indoor air temperatures.

We have also discovered that if the indoor air temperature is correlatedwith the compressor discharge refrigerant temperature instead of theoutdoor air temperature, then the deviation from the baseline thatindicates a low of refrigerant charge could be tightened from 25° F. to20° F., further improving the sensitivity of the RMS to detect evensmaller deviations in performance and even smaller losses of charge.However, our currently preferred embodiment uses only the compressordischarge temperature with the outdoor ambient air temperature sincethis can detect sufficiently small changes in capacity and refrigerantcharge without requiring an additional ED or attempting to measureindoor air temperature with the AP that will be located next to a heatsource (computer) which may distort the temperature reading.

Furthermore, if indoor and outdoor air temperatures are used tocorrelate compressor discharge refrigerant temperature, the offset frombaseline can be further reduced for maximum monitoring precision.

Failure Mode 2: Low Starting Torque Caused by Low Run Capacitance

Three methods can be used to determine if the starting torque isdiminishing due to a faulty capacitor. In the simplest method, the ratioof the start windings voltage to the run winding voltage (or theinverse) as a function of condensing unit or compressor current draw ofthe normally operating baseline system can be compared to the measuredvalue of this voltage ratio over time. A decrease of more than 5% in themeasured voltage ratio value when compared to the baseline normalpredicted value (evaluated at the current draw), indicates a warningthat the capacitance of the run capacitor has degraded and the capacitorshould be replaced even though the unit remains operational. A decreaseof more than 10% in the measured voltage ratio value when compared tothe baseline normal predicted value (evaluated at the current draw),indicates a severe problem since the capacitance of the run capacitorhas degraded to the point that the system may not start on a hot day andthe capacitor should be replaced as soon as possible.

In the currently preferred embodiment, a baseline of the winding voltageratio (start winding voltage divided by run winding voltage or theinverse) versus the total current is established during the learningperiod to detect low run capacitance. After a sufficient learning periodwhen a large enough current range has been completed, a best-fit secondorder polynomial baseline is then calculated. When the winding voltageratio for a given current is less than 95% of the predicted value, a lowpriority warning of low capacitance is indicated. When the windingvoltage ratio is less than 90% of the predicted value, a high prioritywarning of low capacitance is indicated.

In addition to our novel approach, two widely accepted methods areavailable. However these methods would significantly increase cost andcomplexity. One method involves directly measuring the capacitance. Thiscan be accomplished by measuring the voltage and current of thecapacitor and using i=C*dv/dt to calculate the capacitance. This methodis not used in the preferred embodiment because of the extra currentsensor required. The other method is to measure the phase offset betweenthe run winding voltage and the start winding voltage; however thisrequires high-speed sampling and therefore dramatically increasesprocessor speed and data storage requirements. This phase offset willdecrease as the capacitance decreases. We have also discovered that thephase offset variation is less sensitive to the capacitance variationthan the preferred method.

Example 2 Demonstrating the Capability to Identify Low Run Capacitance

FIG. 9 shows the variation in winding voltage ratio as a function ofcurrent at different run capacitances for a condensing unit. Theparticular condensing unit used in this example specified a 45 uF runcapacitor. The normalized winding voltage ratio of a 45 μF capacitor wasused as the baseline data. In this example, the equation for thebaseline curve wasBaseline=−0.0004I ²−0.15I+1.2203where I is the current draw of the unit. The current draw used toestablish the coefficients of the second order polynomial are determinedfrom initial operating data during the learning process and either thecompressor current draw or the current draw of the entire outdoor unitcan be utilized as long as the current being measured is consistent.That is the current draw being used to learn must be the same as thecurrent draw used during subsequent monitoring.

The non-critical and critical alarm curves are at normalized windingvalues of 95% and 90% of the baseline curve, respectively.Non-Critical Low Run Capacitance=0.95*BaselineorNon-Critical Low Run Capacitance=0.95(−0.0004I ²−0.15I+1.2203)Critical Low Run Capacitance=0.90*BaselineorNon-Critical Low Run Capacitance=0.90(−0.0004I ²−0.15I+1.2203)The data was collected at multiple temperatures for each capacitance tovary current draw. It can be seen that the slope of the winding voltageratio to current is the same at lower run capacitances and only they-intercept changes. This observation is used to determine thethresholds which are scaled second order polynomials of the baseline.While a higher order curve fit of the data could of course be used, wehave discovered that a simple second order polynomial curve fit issufficient.Failure Mode 3: Low Starting Torque Caused by Faulty Potential Relay orDegraded Start Capacitor

The same method used in Failure Mode 2 and discussed in Example 2,namely the variation in the winding ratio, is used to identify a low runcapacitance. However for Start Capacitor and Potential Relay monitoring,only the transient change in this behavior during the initial start-upof the compressor is used, since the potential relay switches the startcapacitor out of the circuit rapidly after start up. Alternatively, wecan monitor the time it takes for the start winding to come up torunning voltage as a start cap failure indicator. For the potentialrelay, we can observe the winding voltage ratio after the start windingrises to determine if the relay opened.

Failure Mode 4—Diminished Condenser Airflow

To detect diminished condenser airflow, a baseline curve of condenseroutlet refrigerant temperature (measured on the external surface of thecondenser outlet piping to reduce cost) verses outdoor ambienttemperature is determined in the baseline data collection period. Oncethis second-order best-fit polynomial has been establishedmathematically, the OCU-ED calculates the expected value during A/C unitmonitoring using the outdoor air temperature. If the measured condenseroutlet temperature is more than 6° F. above the predicted value from thebaseline curve (represents 37% blockage), diminished condenser airflowwill be indicated if the compressor discharge temperature is within thenormal range. A condenser coil that is 37% blocked will result in adeviation from the baseline (normal) liquid line temperature curve of 6°F. However, just a deviation from the liquid line temperature baselinecurve is not sufficient to identify decreased condenser airflow becausea system lacking refrigerant charge can also cause a 5° F. increase inliquid line temperature. Therefore, to identify insufficient condenserairflow, as opposed to some other problem, the liquid line must be atleast 6° F. greater than the baseline value and the compressor dischargetemperature must be within 15° F. of the baseline (which indicates theA/C unit is sufficiently charged). While these two tests are sufficientto accurately detect reduced condenser airflow, we have also discoveredthat an additional identifying trait is the increased current draw.Specifically, the current draw can be compared to the baselineperformance current curve and the current draw should be at least 0.3amperes more than the baseline value if the condenser flow is reduced(see Table 2 below). The normal baseline current draw is also evaluatedusing the measured outdoor air temperature).

It will now be understood by one skilled in the art that a key aspect ofthis invention is to use the condenser liquid outlet temperature,measured on the external refrigerant piping just downstream of thecondenser, as an indicator of system problems related to decreasedcondenser airflow if a prior problem of low-charge was not indicated.The actual variation to be used to detect a problem is dependent on thelevel of detection desired by the designer. It should also be noted thatthe condenser liquid line temperature increases with outdoor airtemperature, but indoor air temperature has a negligible effect on thecondenser outlet temperature data as can be seen in (FIG. 8). Theinsensitivity to indoor air temperature is significant since indoor airtemperature is not being monitored in order to reduce system monitoringcost complexity. Once again, to reduce the cost of the temperaturesensor, this condenser refrigerant outlet temperature is measured on theexterior surface of the tubing downstream of the condenser. Since thebaseline behavior is learned after the sensor is installed, the exactlocation of the temperature sensor downstream of the condenser is notcritical, but of course, must be near enough to avoid any temperatureeffects, such as sunlight, which would not be directly related to thecondenser refrigerant exit temperature.

Example 4 Experimental Demonstration of the Faulty Condenser AirflowDetection Method

FIG. 8 displays the baseline, non-critical alarm, and critical alarmcurves for condenser blockages which were calculated after baseline datacollection. The baseline curve equation in this example isBaseline=0.0369T _(amb) ²−5.27T _(amb)+270.10where T_(amb) is the outdoor air temperature.

The non-critical condenser blockage alarm curve and critical condenserblockage alarm curve values are 6° F. and 10° F. greater than thebaseline curve y-intercept.Non-Critical Condenser Air Blockage=Baseline+6orNon-Critical Condenser Air Blockage=0.0369T _(amb) ²−5.27T _(amb)+276.10Critical Condenser Air Blockage=Baseline+10orCritical Condenser Air Blockage=0.0369T _(amb) ²−5.27T _(amb)+280.10

FIG. 8 displays the measured values obtained when operating with each ofthe failure modes identified in Table 1 and how they compare to thethresholds for non-critical and critical arm notifications. As shown inFIG. 8 a condenser coil that is 37% blocked will result in a deviationfrom the baseline (normal) liquid line temperature curve of 6° F.However, as stated earlier, a deviation from the liquid line temperaturebaseline curve is not sufficient to identify low condenser airflowbecause a system lacking one pound of refrigerant charge will also causea 6° F. increase in liquid line temperature. Therefore, to identifyinsufficient condenser airflow, the liquid line must be at least 6° F.greater than the baseline value and the compressor discharge temperaturemust be within 15° F. of the baseline (which indicates the A/C unit issufficiently charged). In this case, the 6° F. offset from baseline willallow early detection of a 37% blocked or restricted airflow condition,which translates into a 1% reduction in cooling capacity and a 7%reduction in the system's Coefficient of Performance. The potentialvariation from the baseline curve, due to not knowing the interiortemperature, has been shown to cause less than a 4° F. differential inliquid line temperature due to indoor air temperature variation (seeFIG. 8), therefore, indoor air temperature need not be monitored. Ofcourse, if the indoor air temperature is known, the tolerances forpredicting a problem can, of course, be improved. A second end devicecommunicating with the existing AP and reporting indoor air temperatureamong other data could of course be implemented within the scope of thepresent invention. This IAH-ED could also be used to both monitor andcontrol the indoor air temperature, by activating the control of thesystem, thereby acting as a thermostat control of the system.

These very small reductions in cooling capacity and performance can bedetected while avoiding the potential for false positives. Note that themaximum temperature differential that can exist due to variations in theunknown interior air temperatures is only 2° F. to 4° F. The 6° F.variation above the baseline was selected to be above the maximumpotential 4° F. normal variation due to different possible normalinterior temperatures. Once again, with the implementation of the indoorair monitoring optional end device, the interior structure temperaturewill be known and the deviation from the baseline can be tightened from6° F. to 4° F., further improving the sensitivity of the RMS to detecteven smaller reductions in cooling capacity and performance.

A complete condenser airflow failure, such as condenser fan failure,will cause condenser saturation temperature to rise until thecompressor's internal cutoff trips due to high electrical current. OurRMS can monitor the number of cycles and cycle duration to identifyshort cycling. In typical RMS operation, the first five minutes of dataare discarded to avoid transient readings. But if an A/C unit shortcycles three consecutive times, (determined by looking at current draw),the RMS will observe the last liquid line temperature to determine ifthe condenser fan has failed. A condenser fan failure will causecondenser liquid line temperatures that are at least 40° F. greater thanthe baseline condenser liquid line temperature.

Failure Mode 5—Diminished Evaporator Airflow

As stated earlier, slight reductions in evaporator airflow must beignored since they can be caused by the use of different quality airfilters at different times. However, should the evaporator airflowbecome significantly reduced due to a dirty air filter or reduced blowerperformance, the RMS will provide an alarm. An 85% blockage of theevaporator airflow rate will result in more than a 0.5 amp decrease inthe compressor current (from the baseline performance curve) and a 5° F.decrease in the compressor discharge temperature. These two concurrentsymptoms are unique to a severely blocked air filter that requireschanging. For example, an 85% reduction in airflow will result in a 25%reduction in cooling capacity and a 17% reduction in COPc.

A total loss of evaporator airflow, caused by a complete blower failure,is indicated by an increase in the compressor discharge temperature ofmore than 10° F. above the baseline curve and a reduction in thecompressor current of more than 1 ampere. These two concurrent symptomsare unique to a blower failure and demonstrate that the A/C unitrequires immediate servicing.

Failure Mode 6—Pitted Contactor

Pitted electrical contact surfaces on the contactor make a poorelectrical connection, causing excessive electrical resistance andsubstantial heating of the contact surface, and resulting in furtherpitting of the contactor. The resistance imposed by the pitted contactorwill lower the voltage to the compressor and condenser fan, providinglower starting and operating torque to these electric motors. Since theRMS measures the voltage both upstream and downstream of the contactor,the voltage drop across the contactor caused can be determined. Thevoltage drop will be divided by the current to determine the contactresistance. An increase in the contactor resistance to more than doublethe originally measured resistance will be flagged as a low-prioritywarning. A contactor resistance of 5 times the original resistance willbe flagged as an immediate high-priority (imminent failure) serviceproblem.

RMS Logic to Generate the Baseline Performance Data

Since thousands of combinations of different condensing units (rated fordifferent efficiencies, power inputs, and refrigerants), air handlers,expansion devices, air filters, and blower motor speed settings exist,it is unrealistic to assume all systems will operate with the sameperformance curves. Therefore, the RMS must learn the performance ofeach individual A/C or heat pump system immediately after RMSinstallation (and after proper A/C system operation is verified by theHVAC technician). The RMS then uses the learned baseline to comparefuture performance. Faults and health monitoring can then be identifiedwhenever the measured performance deviates too far from the establishedbaseline data.

In the currently preferred embodiment, the RMS performs the followingsteps to collect the baseline data (also shown in FIG. 10):

-   -   1) A trained HVAC/R technician installs the RMS device,        completes the system information questionnaire, and activates        the reset switch. This technician or some other employee of the        service provider must enter the system information onto the web        server.    -   2) When the unit starts, the RMS does not take temperature or        voltage and current readings until the OCU has been operating        for a minimum amount of time, to allow the system to reach a        stable operating condition for the current outdoor ambient        temperature. In the currently preferred embodiment, five minutes        of operation has been shown to be sufficient for the sensor        readings to achieve reasonably stable, steady state conditions.    -   3) When the unit is operating within the Temperature Learning        Range, the RMS records the data from each sensor at regular        intervals. In the currently preferred embodiment, the time        interval for temperature readings is 30-seconds and the time        intervals for current and voltage sensors are five-seconds. In        the current embodiment, data is recorded over a five-minute        interval for each data point. When all data storage spaces are        filled at the end of the five minute interval, the next data        point overwrites the oldest piece of data. Therefore, only the        most recent five minutes of data are stored on the OCU-ED. Upon        cycle stop or after one hour of continuous A/C operation, these        recorded data points (for each sensor) are analyzed for        statistical accuracy (to eliminate outliers) and then averaged.        Of course, one skilled in the art could use other data sampling        methods.    -   4) To calculate accurate system performance algorithms over the        typical range of outdoor air temperature during A/C operation,        Baseline Performance Data must be collected over the Temperature        Learning Range. These data are referred to as Baseline        Performance Data. If the baseline performance data sets are not        complete, the OCU-ED will attempt to add the new data point to        the Baseline Performance Data set. If the averaged outdoor air        temperature of the last data point is at least 1° F. from any        existing baseline data point, it is saved as a baseline data        point. Once the last data point is saved to the Baseline        Performance Data or discarded if the data point for that        temperature already exists, the process goes back to Step 2 if        more Baseline Performance Data points are needed or proceed to        Step 5 if the Baseline Performance Data is complete.    -   5) Once Baseline Performance Data is collected, the OCU-ED        either transmits the Baseline Performance Data to the server        (via the AP), and the server then calculates performance        algorithms for each individual sensor, or these calculations can        be performed locally on the OCU-ED. For the currently preferred        embodiment, these algorithms are second-order, best-fit        polynomials of the Baseline Performance Data and describe        acceptable system performance when the unit is operating        correctly. Once Baseline Performance Algorithms are calculated        with respect to outdoor air temperature, they can be saved on        the server, downloaded for storage on the OCU-ED, or both.

The Learning Process can be completed in as little as one day/nightoperation of the A/C unit. The system can relearn the A/C unit anytime aservice technician believes a major repair or tune-up to the system hasoccurred and the Relearn Switch has been actuated. This can beaccomplished by pressing the momentary reset switch or via a softwaresetting.

After performance data is analyzed and averaged, all data collected inthe future is compared to the Baseline Performance Algorithms. Thiscomparison can be performed locally and/or remotely. Faults areidentified when the new data fall too far from the expected performancethat is calculated using the outdoor air temperature and BaselinePerformance Algorithms.

A Currently Preferred Embodiment of the RMS Health Monitoring Logic

Given the disclosure herein, one skilled in the art can now envisionother ways to compare the measured data with the baseline performancecurves. One currently contemplated and preferred approach is nowdescribed (FIG. 11).

Once the RMS has learned a particular system:

-   -   1) Using polynomials to curve fit the learned normal behavior,        the OCU-ED or the host computer calculates the expected        compressor discharge temperature, condenser liquid line outlet        temperature, and condensing unit (or compressor) current draw        for the particular measured outdoor air temperature. In the        currently preferred embodiment, a second order polynomial is        used to fit this data. Using a polynomial, the OCU-ED or the        host computer calculates the expected start winding to run        winding voltage ratio for the particular measured current. In        the currently preferred embodiment, a second order polynomial is        used to fit this learned normal voltage ratio data.    -   2) The data collected at the end of every A/C system cycle (the        last 5 minutes of operation is captured using the same method        used in the learning process) is compared to the Baseline        Performance Value (determined at the average outdoor air        temperature or current).    -   3) If the last data point falls too far from the expected        baseline data point, the OCU-ED sends a packet of information to        the AP to be relayed to the host computer (the server), and the        reporting frequency is increased.    -   4) The server processes the data to ensure they are consistent        and repeatable before raising an alarm.        A Currently Preferred Embodiment to Determine Critical or        Non-critical Alarm Status

The RMS can identify not only A/C system problems, but also categorizethe severity of the problem depending on the potential for an immediatefailure. High priority critical alarms have the potential to damage A/Cequipment, fail immediately, or cause mold problems since buildinghumidity is not being controlled. These failed systems must be servicedimmediately. Lower priority alarms refer to situations causinginefficient operation or decreased cooling capacity, but immediateservicing is not required to prevent equipment damage or eminentfailure. These alarm distinctions allow the HVAC technician toprioritize the service calls by servicing critical alarms first and thenunits with non-critical alarms when they have time.

Contractors and equipment owners do not want an RMS that produces falsealarms or fails to identify problems. Therefore, we have developed thefollowing features in the described embodiment to eliminate thepossibility of false alarms or unidentified problems:

-   -   Eliminate transient effects—The RMS OCU-ED will discard data        collected during the first five minutes of operation and will        only analyze data collected during the last five minutes of        operation. Experimental data showed that the time-averaged data        of the first five minutes of operation did not accurately        represent system performance. However, the system performance        from five to ten minutes after cycle start was an accurate        representation of steady-state performance.    -   Collect several data points and obtain average values—The RMS        will store the last ten data points for each sensor to allow        time-averaging over a five-minute span of operation.    -   To assure the data recorded represents steady state and not        transient data, the data will be obtained after the unit has        been operating for a sufficient period of time, typically more        than five minutes of operation. One method to do this is to        continually record the last five minutes of data, overwriting        the same data storage locations. In this way, the last data        saved, represents the data that was collected during the last        five minutes of operation (just before the A/C is cycled off).        For long periods of operation, the last five minutes of every        hour of uninterrupted operation can be used. These methods are,        generally speaking, well known in the art.    -   Eliminate spurious data points—Prior to time-averaging the data        points, the RMS will perform simple statistical verification to        the data and eliminate any outliers that may skew the averages.        If the data scatter is too large, the entire data set will be        repeated.    -   The baseline data performance curves are only meant to be        accurate within the 70° F. to 95° F. outdoor air temperature        range. Increasing this temperature range would require        unacceptable extrapolation or baseline data collection that        could last months. Therefore, data points with outdoor air        temperature averages that fall outside of the Temperature        Learning Range are discarded. While some data points on cooler        or hotter days will be discarded, data will be collected within        the Temperature Learning Range during the afternoon, night,        and/or morning of those same days so that alarm conditions will        still be promptly identified without inaccurate extrapolation.    -   One individual alarm reading will not trigger the alarm        notification. In the current embodiment, three consecutive alarm        readings for the same critical problem are required to trigger a        critical alarm, while ten consecutive alarms are required for        non-critical alarm notification.

Table 2 briefly summarizes A/C unit conditions that can be identified,the way in which the RMS identifies the condition, the accuracy of thedetection, and the system inefficiency when the problem is identified.

TABLE 2 Ability of RMS to detect power consumption increase or coolingcapacity degradation Condition Means of Identification DetectionAccuracy Low Compressor discharge 1 lb low charge refrigerant temp >baseline + 25° F. 13% reduced capacity charge 5% reduced COPc Failed RunWinding Voltage 28% reduction in run Capacitor Ratio < 0.95 capacitanceBlocked or Liquid line temp > 37% condenser blockage RestrictedBaseline + 6° F. AND 1% reduced capacity Condenser Current draw > 7%reduced COPc Airflow Baseline + 0.3 A. AND Compressor discharge temp <baseline + 15° F Blocked or Current draw < 80% blockage RestrictedBaseline − 0.5 A AND 12% reduced capacity Evaporator Compressordischarge 9% reduced COPc Airflow temp < baseline − 5° F. Pitted VoltageDrop Across the Any significant increase in Contactor Contactor andcurrent flow contactor resistance (>5%)

While we have shown and described a currently preferred embodiment ofour invention, it should be understood that the same is susceptible tochanges and modifications without departing from the scope of ourinvention. For example, one skilled in the art will readily appreciatethat this invention will work for any vapor compression thermal controlsystem including but not limited to refrigerators, freezers,cryocoolers, air conditioners, dehumidifiers, heat pumps, water coolers,and the like. Therefore, we do not intend to be limited to the detailsshown and described but intend to cover all such changes andmodifications as are encompassed by the scope of the appended claims.

We claim:
 1. A monitoring system for at least one vapor-compressionsystem having an outdoor section comprised of a compressor and acondenser, wherein the monitoring system comprises at least two sensorsassociated with only the outdoor section so that a processed output ofthe sensors is able by itself to predict low evaporator air flow basedon predicted sensor values determined at a current outdoor ambienttemperature by comparison with one of a previously obtained measuredperformance curve, a table of values and an equation, each as a functionof outdoor ambient air temperature obtained during normal operation ofthe vapor-compression system.
 2. The monitoring system of claim 1,wherein the evaporator airflow is projected to be undesirably low whenone of the predicted sensor values is representative of one of thecompressor discharge or compressor inlet refrigerant temperature, andanother of the predicted sensor values is representative of a currentdraw of one of the compressor and a combined current draw of the outdoorsection current draw of one of the compressor, and the measuredcompressor temperature is more than a predetermined offset amount belowa predicted normal operation temperature and the current draw is morethan a predetermined current offset amount below the predicted normaloperation current.
 3. The monitoring system of claim 2, wherein themeasured compressor discharge temperature is an external surfacetemperature of the compressor discharge tube.
 4. The monitoring systemof claim 2, wherein the measured compressor inlet temperature is anexternal surface temperature of the compressor inlet tube.
 5. Themonitoring system of claim 2, wherein the temperature offset amount forthe compressor discharge temperature is 5 degrees F., and the currentoffset for the current draw is one half an ampere.
 6. The monitoringsystem of claim 2, wherein the temperature offset amount for thecompressor inlet temperature is 5 degrees F., and the current offset forthe current draw is one half an ampere.
 7. The monitoring system ofclaim 1, wherein data concerning an occurrence of periods when the atleast one vapor compression system is operating with an undesirablyreduced evaporator airflow is transmitted via the Internet to at leastone of the vapor compression system's custodian and a repair serviceprovider.